1. Field of the Invention
The present invention generally relates to control systems for automatic transmissions. More specifically, the present invention relates to an automatic transmission control system that controls the hydraulic pressure in an automatic transmission during shifting at low temperatures.
2. Background Information
Automatic transmissions have been proposed in which hydraulic pressure is controlled at low temperatures during shifting to avoid shift shock. For example, Japanese Patent Application Laid-Open Publication No. 10-103483A discloses an automatic transmission that uses such hydraulic pressure control at low temperatures during shifting to avoid shift shock. In particular, because the fluidity of automatic transmission hydraulic fluid drops at low temperatures, the response characteristics of hydraulic pressure supplied to frictional elements (e.g., clutches, brakes, etc.) are reduced and shift shock occur. In view of this situation, the conventional technology described in this above-mentioned patent publication proposes to determine an end timing of a so-called precharge control based on a rate of change of turbine rotational speed in order to avoid occurrence of rapid engagement shocks.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved automatic transmission control system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.